For a progressive wave on a stretched string, state what is meant by amplitude.

1. (a)For a progressive wave on a stretched string, state what is meant by amplitude.[1]
2. (b)Light from a laser has a wavelength of 690 nm in a vacuum. Calculate the period of the light wave.[3]
3. (c)A two-source interference experiment uses the arrangement shown in Fig. 5.1. [Figure 5.1] Light from a laser is incident normally on a double slit. A screen is parallel to the double slit. Interference fringes are seen on the screen at distance D from the double slit. The separation of the centres of the slits is a. The light has wavelength λ. The separation x of the centres of adjacent bright fringes is measured for different values of distance D. The variation with D of x is shown in Fig. 5.2. The gradient of the graph is G. [Figure 5.2]
4. (c)(i)Determine an expression, in terms of G and λ, for the separation a of the slits.[2]
5. (c)(ii)The experiment is repeated with slits of separation 2a. The wavelength of the light is unchanged. On Fig. 5.2, sketch a graph to show the results of this experiment.[2]

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